Homonymous Hemianopia, Occipital Lobe, Temporal Crescent

Diagnosis:

Homonymous Hemianopia, Occipital Lobe, Temporal Crescent

Comment to photo:

This is an incomplete right inferior quadrantanopia with a very unusual feature. In the extreme temporal periphery OD is a tongue of preserved field that projects downward and partially encloses the hemianopic defect in that eye.
Recall that in each eye, the portion of the temporal field between sixty and ninety degrees from fixation has no correlate in the nasal field of the fellow eye. This so-called “temporal crescent” projects to the anterior portion of the contralateral occipital lobe where it is susceptible either to selective damage or to selective sparing by disease processes. Accordingly, the observation of partial or complete sparing of the temporal crescent implicates the occipital lobe as the site of pathology.